US 20070129623 A1
An apparatus (180) for measuring intraocular pressure (IOP) comprises a contact lens (40) including an inner surface (42) contoured to a surface portion (34) of an eye (36) and a sensor (10) disposed in the contact lens. The sensor (10) comprises a contact surface (14) for making contact with the surface portion (34) of the eye (36). The contact surface (14) includes an outer non-compliant region (16) and an inner.compliant region (18) fabricated as an impedance element that varies in impedance as the inner compliant region changes shape. The sensor (10) further comprises a region of conductive material (38) electrically coupled to the impedance element of the compliant region (18) and responsive to an external signal for energizing the impedance element so that the IOP may be determined.
1. An apparatus for measuring intraocular pressure of an eye, said apparatus comprising:
a contact lens including an inner surface contoured to a surface portion of the eye for engaging the surface portion; and
a sensor disposed in said inner surface of said contact lens, said sensor comprising:
a contact surface for making contact with the surface portion of the eye, said contact surface including an outer non-compliant region and an inner compliant region fabricated as an impedance element that varies in impedance as said inner compliant region changes shape; and
a region of conductive material electrically coupled to said impedance element of said compliant region and responsive to an external signal for energizing said impedance element so that the intraocular pressure may be determined.
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This application is a continuation-in-part of a co-pending U.S. patent application Ser. No. 09/642,573, entitled “SYSTEM FOR MEASURING INTRAOCULAR PRESSURE FOR AN EYE AND A MEM SENSOR FOR USE THEREWITH”, filed Aug. 21, 2000. The subject matter of the aforementioned co-pending application is incorporated herein by reference.
The present invention relates to a system for measuring intraocular pressure (IOP) in an eye, and is particularly directed to a system for measuring IOP that utilizes a sensor fabricated through microelectromechanical system (MEMS) technology and which is mounted in a contact lens.
Glaucoma patientscand post-operative patients of eye surgery require regular monitoring of the IOP of their eyes in order to diagnose degenerative conditions which may lead to degraded sight and/or blindness without immediate medical treatment. Accordingly such patients must make frequent trips to their ophthalmologist's. office for this regular monitoring of their IOP with conventional mechanical impact type tonometers. This becomes a nuisance to the patient after a time leading to patient resistance to compliance. In addition, the only measurement of the patient's IOP that the doctor can use for diagnosis is the pressure that exists at the time of the office visit. Therefore, if the pressure is normal at the time of the visit, but becomes high thereafter, the patient's actual risk of blindness may be misdiagnosed. Also, if the pressure measured at the time of the office visit is high for reasons other than eye degeneration, the patient may be falsely diagnosed and be required to undergo therapy that may not be needed.
Intraocular pressure has been known to fluctuate widely during any given period of time and thus, should be monitored many times during the period of a day in order to gain an average or representative IOP which in turn may be tracked for diagnosis. Attempts have been made to permit glaucoma patients to monitor their IOP at home many time during the period of a day with a self-tonometry portable instrument. Reference is made to the paper “Self-Tonometry to Manage Patients with Glaucoma and Apparently Controlled Intraocular Pressure”, Jacob T. Wilensky et al., published in Arch Ophthalmol, Vol. 105, August 1987 for more details of such a device. This paper describes a portable, tonometer instrument consisting of a pneumatically driven plunger, fitted with an elastic membrane, that slowly comes forward and applanates the cornea. Applanation is detected by an internal optic. sensor and the pressure necessary to achieve applanation is registered and displayed automatically. The patient is able to prepare the eye and self-tonometer and activate the instrument for taking the measurement. However, the device proposed is relatively large and bulky, about the size of an attache+ case, for example, and not conducive to convenient transport with the patient during normal daily routine in order to measure IOP. In addition, the proposed technique requires special eye preparation by instilling a topical anesthetic in the eye prior to tonometric measurements.
Also, very crude attempts have been made to develop methods of non-invasively monitoring IOP using passive electronic circuitry and radiotelemetry disposed at the eye. In the papers of R. L. Cooper et al. namely, those published in Invest., Ophthalmol Visual Sci., pp. 168-171, Feb. 1977; British JOO, 1979, 63, pp. 799-804; Invest, Ophthalmol Visual Sci., 18, pp. 930-938, September, 1979; and Australian Journal of Ophthalmology 1983, 11, pp. 143-148, a miniature guard ring applanating transsensor (AT) which included electronic components that changed in resonance proportional to the IOP was mounted in an acrylic or sauflon haptic contact lens element that was individually designed for the human eye. The AT was mounted in the lower part of the scleral haptic so that it applanated the inferior sclera under the lower lid. The whole haptic ring was placed in the conjunctival fornix. IOP was monitored from the AT with an automatic continual frequency monitor (ACFM) attached by adhesive and elastic bands to the exterior of the lower eye lid. The ACFM induced in the AT electromagnetic oscillations at varying radio frequencies via a magnetic coupling of inductive coils and monitored for its resonant frequency representative of IOP. This device is clearly uncomfortable and bulky, minimizing expected patient compliance. In addition, the device measures IOP by applanation of the sclera, which is a rather unconventional method of measuring IOP.
In another paper reported in Investigative Ophthalmology Reports, pp. 299-302, April, 1974 by B. G. Gilman, a device is presented for measuring IOP of a rabbit in a continuous manner with strain gauges mounted (embedded) in soft flush fitting, silastic gel (hydrogel) contact lenses. The exact shape of the eye of the rabbit was obtained by a molding procedure. Leads of the strain gauges extended from the lens and were connected to a wheatstone bridge arrangement for measurement taking. The paper suggests that the embedded strain gauges may be used with a miniature telemetry package completely contained in a hydrophilic hydrogel contact lens for continuous, noninvasive, long duration monitoring of IOP, although no design was provided. This device proposes wire connections for telemetry which entails wires to be run out of the eye under the eyelid. Also, the proposed approach requires the molding of a special contact for each individual eye, a practice which would make widespread use unattractive and expensive.
In 1993, an IEEE paper was presented by C. den Besten and P. Bergveld of the University of Twente, The Netherlands, proposing a new instrument for measuring area of applanation entitled “A New Tonometer Based on Application of Micro-Mechanical Sensors”. This new instrument is based on the Mackay-Marg principle of tonometer operation in which a plate having a diameter of 6mm or less is pressed against and flattens a portion of the cornea of the eye, referred to as “applanation”. In the middle of the plate is a small pressure sensitive area that is pressed against the flattened portion of the cornea with a slowing-increasing force while the pressure area is electronically measured. The applanation sensor of this new instrument comprises a micro-machined plunger and pressure sensing electronics on three electrically insulated levels of a silicon substrate resulting in a modified Mackay-Marg tonometer in which the radius of the flattened area and the distanc e between the periphery of the applanation and the pressure center can be measured to render a more accurate pressure area measurement. In the work presented in this paper, the researchers did not actually propose a pressure sensor or transducer. In addition, it is not clear if, for as long as the eye is applanated, there is a need to know the area of applanation. Sufficient applanation is usually determined by the difference in trough height from the peak to dip of the pressure profile. The dip is unlikely to occur unless sufficient applanation is achieved.
Also, in the U.S. Pat. No. 5,830,139 entitled “Tonometer System for Measuring Intraocular Pressure by Applanation and/or Indentations”, issued to Abreu on Nov. 3, 1998, a tonometer system is disclosed using a contact device shaped to match the outer surface of the cornea and having a hole through which a movable central piece is slidably disposed for flattening or indenting a portion of the cornea. A magnetic field controls the movement of the central piece against the eye surface to achieve a predetermined amount of applanation. A sophisticated optical arrangement is used to detect when the predetermined amount of applanation has been achieved to measure IOP and a calculation unit determines the intraocular pressure based on the amount of force the contact device must apply against the cornea in order to achieve the predetermined amount of applanation. The magnetic and optical arrangements of this device requires special alignment and calibration techniques rendering it difficult for use as a self-tonometry device.
While the various foregoing described U.S. patent and papers propose various devices and instruments for tonometry, none appears to offer a viable inexpensive, convenient solution to the immediate problem of seif-tonometry. The present invention overcomes the drawbacks of the proposed instruments described above to yield a simple, inexpensive and easy to use instrument that completely automates the tonometry process and offers post-processing of tonometer IOP readings from which a proper elevation and diagnosis by an ophthalmologist may be performed.
The present invention is an apparatus for measuring intraocular pressure of an eye. The apparatus comprises a contact lens including an inner surface contoured to a surface portion of the eye and a sensor disposed in the inner surface of the contact lens. The sensor comprises a contact surface for making contact with the surface portion of the eye. The contact surface includes an outer non-compliant region and an inner compliant region fabricated as an impedance element that varies in impedance as the inner compliant region changes shape. The sensor further comprises a region of conductive material that is electrically coupled to the impedance element of the compliant region and responsive to an external signal for energizing the impedance element so that the intraocular pressure may be determined.
The present invention also provides a method for measuring intraocular pressure (IOP) of an eye. According to the inventive method, a contact lens is provided with an inner surface contoured to the eye. The contact lens includes a sensor disposed in the inner surface of the contact lens. The sensor has a compliant region that functions as an impedance element. The contact lens is positioned on the surface portion of the eye. An applanator is provided for applying pressure against the contact lens. The applanator is moved toward the eye until the sensor forcefully engages the surface portion of the eye which causes the compliant region to change shape and vary in impedance. The impedance element is energized and a representative pressure measurement is determined each time the impedance element is energized. The representative pressure measurements are processed to render a resultant IOP measurement.
The foregoing and other features of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which:
FIGS. 6(a 1)-6(i 2) are cross-sectional and plan views, respectively, of the tonometer sensor through various stages of a fabrication process;
FIGS. 7(a 1)-7(j 2) are cross-sectional and plan views, respectively, of an alternate tonometer sensor through various stages of a fabrication process;
FIGS. 8(a 1)-8(d) are cross-sectional and plan views of another alternate tonometer sensor through various stages of a fabrication process;
FIGS. 11A1-11E2 are illustrations of the response of the apparatus of
A tonometer sensor 10 produced using microelectromechanical system (MEMS) techniques is shown in
As shown by the substrate cross-sectional and plan views of
In the present embodiment, the inductor coil 38 is formed by disposing conductive material in a predetermined pattern, like a concentric spiraled pattern, for example, in the non-compliant region 16. A process for fabricating the inductor coil 38 at the non-compliant region 16 is described in greater detail herein below. However, it should be understood that the inductor region need not be embodied solely at the non-compliant region 16 and may be embodied as part of the compliant region 18 as well without deviating from the principles of the present invention. Further, it should be understood by those of ordinary skill in the art that there could be a spiral inductor 42 on the contact surface 14 of the diaphragm 20 coupled to a flat spiral inductor 44 underneath the diaphragm as illustrated in the alternate embodiment of
In the present embodiment, the resonant circuit comprising the inductor coil 38 and the capacitive element formed by the plates 20 and 24 may be excited into resonance by an external electromagnetic signal in the radio frequency (RF) range. Tank circuits of this type have a natural resonant frequency fo that, to the first order, depends of the values of the inductor and the capacitor as follows:
For example, if the contact area 14 of the tonometer sensor 10 is approximately one square millimeter (1 mm2) or one millimeter (1 mm) on each side, the diaphragm 20 of the compliant region 18 may have a diameter of five hundred micrometers (500 μm) with a one and a half micrometer (1.5 μm) dielectric or air gap, and the inductor coil may have twenty-five (25) turns with an inside diameter (ID) of five hundred micrometers (500 μm) and an outside diameter (OD) of one thousand micrometers (1,000 μm). With the diaphragm 20 undisturbed, the resonant frequency may be on the order of one hundred and ninety-three megahertz (193 MHz). Accordingly, a ten percent (10%) increase in capacitance, for example, resulting from a diaphragm 20 deflection will produce a downward shift in resonant frequency to one hundred and eighty-four point one megahertz (184.1 MHz) and this shift in resonant frequency is readily discernible electronically as will be further described herein below. It is understood that the contact area of the sensor 10 may be less than 1 mm, in which case the various dimensions may be rescaled proportionately.
As has been described in connection with the illustration of
An exemplary process suitable for fabricating an embodiment of the tonometer sensor 10 is shown in the process diagrams of FIGS. 6(a 1) through 6(i 2) wherein each Figure provides cross-sectional and plan views, respectively, of the sensor structure at various stages of the fabrication process. The process starts with a substrate 100 which may be part of a silicon wafer, for example, as shown in
In the step of
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As shown in
An embodiment for illustrating a fabrication process of an alternate embodiment of the tonometer sensor 10 is shown in the FIGS. 7(a 1) through 7(j 2) wherein each Figure provides cross-sectional and plan views, respectively, of the alternate sensor structure at various stages of the fabrication process. The process starts with a substrate 140 which may be part of a silicon wafer, for example, as shown in
Next, in the step of
The top surface 142 of the resulting structure as shown in
In the step of
In the step of
Next, in the step of
While the present MEMS sensor 51 is described as being fabricated on a silicon substrate, it is understood that other substrates may be used such as a polymeric material, including plastics and polymer films, for example. Such an alternate MEMS sensor 51 could be fabricated using a well-known micro-replication process such as is illustrated in FIGS. 8(a)-8(d), with the simultaneous fabrication of two of the sensors 51 being shown side by side. In FIGS. 8(a 1) and 8(a 2), a thin film of plastic or polymer is mechanically patterned, preferably with dimples that would represent wells 54, by a conventional process. The film 52 would then be metalized to form a ground electrode 56. A second film 58 (
Referring now to
The sensor 10 may be incorporated into the contact lens 40 at the inner surface 42 during the lens fabrication process. For example, if the contact lens 40 is made using a spin casting process, the lens solution is injected onto a spinning mold (not shown), with the spin rate and time being typically computer controlled. The sensor 10 may be placed in a pocket machined into the mold and held in place via vacuum. When the molding is complete, the vacuum is removed from the sensor 10, the contact lens 40 is removed from the mold and the contact lens with the sensor incorporated therein is handled using conventional procedures. Accordingly, the contact lens 40 including the sensor 10 may be a separate article of manufacture in accordance with one aspect of the present invention.
The apparatus 180 further comprises a hand-held eyepiece 182 with a relatively movable applanator 184 for manually applying force against the sensor 10 as described further below. The eyepiece 182 includes upper and lower arcuate ridges 184 and 186 for aligning the eyepiece in the patient's eye socket. The eyepiece 182 further includes an antenna 187 (shown schematically in
The applanator 184 resembles a plunger disposed in a cylinder and has a distal end 185. The distal end 185 is movable toward the eye 36 relative to the eyepiece 182 by pushing manually on a pushbutton mechanism 188. Internally, the motion of the applanator 184 may be opposed or biased by a spring (not shown) and/or a damper (not shown). Further, it is contemplated that movement of the pushbutton mechanism 188 may pressurize a balloon (not shown) inside the applanator 184 that causes the distal end 185 of the applanator to move toward the eye 36. Similarly, a bladder (not shown) of silicone gel could be compressed inside the applanator 184 by pressing the pushbutton mechanism 188 to cause the distal end 185 to move toward the eye. It is also contemplated that the applanator 184 could include a motorized and/or automated mechanism that is actuated by pressing the pushbutton mechanism 188 and which presses the distal end 185 against the eye 36.
As may be seen in
When the contact surface 14 of the sensor 10 is pressed against the surface portion 34 of the eye 36, the response of the sensor 10 over time is shown in the illustrations of FIGS. 11A1 through 11E2. Each of the FIGS. llA through 11E provides an illustration of the position of the sensor 10 in relation to the eye 36 and a corresponding time graph of a pressure representative signal vs. time. The darkened region along each time graph is the time interval represented by the respective illustration. In
Accordingly, as the sensor 10 is pressed further against the surface portion 34 and the diaphragm 20 is depressed as shown in
In order to take the IOP measurements from the sensor 10, a control unit 50 (
A schematic block diagram of the control unit 50 for use in of the present invention is shown in
The voltage across the inductor L1 is input to another RF amplifier 222 via signal line 224. The output 226 of the RF amplifier 222 is provided to a root-mean-square (RMS) detector 228, the output 230 of which being coupled to a comparator circuit 232. In the present embodiment, the comparator circuit 232 functions as a signal peak or valley detector and generates a signal over line 234 when the signal peak or valley is detected. The signal line 234 is coupled to the counter 218 and output buffer 220 for operation thereof. The circuits of the control unit 50 may be centrally controlled in operation by a digital controller 240, which may be a programmed microprocessor, digital signal processor or a combination of hardwired digital logic circuits. A memory unit 242 is coupled to the digital controller 240 and may be comprised of a combination of static, dynamic and read-only memory units, for example, for the storage of data and program information. A switch 244 is coupled to the digital controller 240 through conventional input-output circuitry (not shown). The digital controller 240 may also be coupled to a conventional display unit 246 for displaying IOP readings. The control unit 50 may also include an upload/download circuit 250 for transmitting data between the digital controller 240 and an external computer, like a PC, for example, over a hardwired connection.
Taking an IOP reading using the sensor 10, including the apparatus 180 and the control unit 50, will now be described in connection with
With the patient's eyelids 190 closed, as may be seen in
As the applanator 184 is being moved toward the eye 36 as shown in
From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, it is contemplated that the applanator 184 could be disposed on the end of an instrument in a doctor's office, rather than a hand-held unit. It is further contemplated that other physical configurations of the applanator 184 could be used, such as a finger-mounted device which would, of course, include the antenna 190. Finally, it is conceivable that closed eyelids 190 may be able to supply sufficient pressure on their own to press the sensor 10 against the eye 36, in which case the eyepiece 182 would carry only the antenna 190 and not the applanator 184. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.